CRYPTOGRAPHY (from Greek kryptós, "hidden", and gráphein, "to write") is, traditionally, the study of means of converting information from its normal, comprehensible form into an incomprehensible format, rendering it unreadable without secret knowledge — the art of encryption. In the past, cryptography helped ensure secrecy in important communications, such as those of spies, military leaders, and diplomats. In recent decades, the field of cryptography has expanded its remit in two ways. Firstly, it provides mechanisms for more than just keeping secrets: schemes like digital signatures and digital cash, for example. Secondly, cryptography has come to be in widespread use by many civilians who do not have extraordinary needs for secrecy, although typically it is transparently built into the infrastructure for computing and telecommunications, and users are not aware of it.

The study of how to circumvent the use of cryptography is called cryptanalysis, or codebreaking. Cryptography and cryptanalysis are sometimes grouped together under the umbrella term cryptology, encompassing the entire subject. In practice, "cryptography" is also often used to refer to the field as a whole; crypto is an informal abbreviation.

Cryptography is an interdisciplinary subject, drawing from several fields. Before the time of computers, it was closely related to linguistics. Nowadays the emphasis has shifted, and cryptography makes extensive use of technical areas of mathematics, especially those areas collectively known as discrete mathematics. This includes topics from number theory, information theory, computational complexity, statistics and combinatorics. It is also a branch of engineering, but an unusual one as it must deal with active, intelligent and malevolent opposition (see cryptographic engineering and security engineering).

Associated fields are steganography — the study of hiding the very existence of a message, and not necessarily the contents of the message itself (for example, microdots, or invisible ink) — and traffic analysis, which is the analysis of patterns of communication in order to learn secret information.

A DEAD DROP is a location used to secretly pass items between two people, without requiring them to meet.

Spies have been known to use dead drops, using various techniques to hide the items and to signal that the drop has been made.

Dead drop spike

The dead drop spike is a concealment device which has been used since the late 1960s to hide money, maps, documents, microfilm, and other items. The spike is waterproof and mildew-proof and can be shoved into the ground or placed in a shallow stream to be retrieved at a later time.

A CUT-OUT is a courier or mechanism used to pass information and espionage related devices from one spy to another while operating in a "denied area" or a hostile environment. There are two forms of cut-outs: block and chain. A block cut-out is an agent familiar with the entire spy network or cell and those who are in it, while the chain cutout is simply an agent who is aware of only the person providing the information and the spy who is receiving the information. The chain cut-out helps to maintain the compartmentalization of the spy network, which increases security by maintaining everyone's anonymity.

EAVESDROPPING is the intercepting and reading of messages and conversations by unintended recipients. One who participates in eavesdropping, i.e. someone who secretly listens in on the conversations of others, is called an eavesdropper. The origin of the term is literal, from people who would literally hide out in the eaves of houses to listen in on other people's private conversations.

Eavesdropping can also be done over telephone lines, email, instant messaging, and any other method of communication considered private. (If a message is publicly broadcast, witnessing it does not count as eavesdropping.)

Messages can be protected against eavesdropping by employing a security service of confidentiality (or privacy). This security service is usually implemented by encryption.

In ancient China, it is said that to act against eavesdropping, when discussing important matters, soldiers would instead draw the characters on hands or papers.

The Canadian heroine Laura Secord is famous for having eavesdropped the plans of American army and delivered this information to the British.

AGENT HANDLING includes the spotting, assessment, recruitment, and direction of the foreign field agent. Often the method of inducing agents into the espionage trade involves the use of money, ideology, compromise, and ego (MICE concept).

Agents are almost always a foreign national who is under the direction of an agent handler or controller. In the case of the U.S. Central Intelligence Agency, this handler is known as a Case Officer, while in the former KGB a controller was known as a Resident.

The spotting of potential agents was often conducted through the skimming of trade journals and professional proceedings for subject experts names and affiliations, vulnerable political and technical delegation members, trade conferences attendees, and foreign travellers whose activities made them potential subjects for blackmail or inducement.

The assessment of potential agents include the verification of their credentials and bona fides or true identities. A risk analysis may also be conducted to determine the dangers of approaching the targeted individual with a 'pitch' for recruitment. This was either done 'cold,' where recruiters have had no prior contact with the target, or 'warm,' inwhich the handler and the target were prior acquaintances. Recruitment of an agent can take many months or even years to accomplish.

After recruitment agents are given the training required for them to conduct espionage activities safely and effectively while operating in a hostile or denied country. They are trained in various tradecraft that can include clandestine communications, elicitation, surveillance and counter surveillance, skydiving, photographic and audio recording, concealment device construction, demolitions, and the use of small arms.

Agent handlers also provide agents with false identities, known as covers or legends that aid them in their access and operability within a denied country. To maintain thier false identities agents use disquises, false or reproduced documentation, pocket litter, dead letter boxes, and other identity support techniques.

However, real history shows that after a source (agent) has been exploited, he is often no longer handled well by many services e.g. BND, MI6 and others. In reality agents are given incentives and promises are made which then turn out to become broken. Since probably every major service can be assumed to be penetrated by moles, every agent runs the risk of being tipped off, which happens frequently after major defectors change sides. As an agent you need a good spymaster to keep this from happening. Norbert Juretzko of BND got sacked after they found he did not file the real names of his Russian spies, keeping them from being shot after KGB received their filed names.

Valuable spies are sometimes not hanged but exchanged for spies from the opposite country. Many agencies tell their spies that they will not be forgotten in a foreign prison, but this is not always the case. During the Cold War many exchanges with eastern-bloc agents were made on the "Glienicke bridge" in Berlin (West).

INTERROGATION is the professional police and military technique of interviewing people, often without their consent, in order to obtain information regarding crimes or military operations.

Interrogation may involve humiliation, intimidation and physical abuse to "soften up" the person interviewed.

A well-conducted interrogation is not torture, which in practice is widely known to be ineffective at producing reliable information. Prisoners of war routinely undergo interrogation, which the laws of war permit.

A typical interrogation involves three people:

• interviewer
• interviewee
• notetaker

The interviewer, who asks the questions, typically sits directly face-to-face with the interviewee (the person under interrogation), while the notetaker sits to the side of the interviewee (usually on the interviewee's right-hand side). The notetaker remains out of view of the interviewee and attempts to remain as silent and inconspicuous as possible.

The interviewer usually asks short open-ended questions and attempts to establish a friendly rapport with the interviewee, and speaks with a neutral and sympathetic voice. The notetaker watches the interaction between the interviewer and the interviewee, paying particular attention to behavior and body language.

One notable interrogation technique is the Reid technique.

Note that no prohibition forbids the interrogator from lying, from making misleading statements or from implying that the interviewee has already been implicated in the crime by someone else. Deception forms an important part of effective interrogation.

However, threats which the interrogator cannot actually carry out are generally ineffective unless the subject is young, inexperienced or terrified.

An important legal protection against interrogation in the United States of America is the right to remain silent and to demand the presence of a lawyer. (See also "Miranda warning".)

Interrogation methods used at Guantanamo Bay for illegal combatants could, with special approval, include sleep deprivation, exposure to extremes of cold and heat, and placing prisoners in "stress positions" for agonizing lengths of time.

A HONEY TRAP is a form of sting operation, in which wrong doers are lured into revealing themselves to a policing organisation. Where a sting operation targets a known or suspected individual and attempts to trap them committing a specific case of crime, a honey trap establishes a general lure to attract unknown criminals.

So for example, the police might fit a car with hidden cameras and leave it in an area known for its problems with car crime as a honey trap. The expectation being that the car will eventually be stolen, recording the evidence in the process.

On the internet, the Honeynet Project (http://project.honeynet.org) attempts to attract and watch hackers breaking in to a number of network systems. In particular it monitors changes in routine and automated hacker activity, such as port scanning. 

The term is also used in detective novels and espionage novels to describe a trap using some form of sexual enticement.

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